USE OF MICROBEADS TO ESTIMATE THE ABSOLUTE ABUNDANCE OF
NANNOFOSSILS

Hisatake Okada, Dept. of Earth Sciences, Yamagata University, Japan
Unless your project is purely biostratigraphical, and nothing else, it is very important to know theabsolute abundance of nannofossils (number/volume of nannofossils per unit volume/weight ofsediment) in each sample. Because of the minute size of nannofossils, however, we can not easily
obtain an absolute "nannofossil number", as foraminiferal workers can. A realistic alternative for us
is to get a relative abundance that can be used as a proxy for the absolute abundance. You can obtain
the proxy abundance by counting nannofossils per given area of slide, but only if you can always
make slides with uniform and consistent densities, which is almost impossible even for one person,
and absolutely impossible between different workers.
Here I would like to introduce a new technique to obtain a proxy value for absolute abundanceby mixing a measured weight of microbeads with the sample. The microbeads I have been
experimenting with are MB-10; these are soda-ash glass spheres (s.g. 2.5g/cm 3) from 2 to 10 J.Lm indiameter. These microbeads have been manufactured as a filler for precision casting. Most packagesof microbeads on the market are manufactured for mixing with paint, for use on night-time reflective
road markings, these usually contain larger beads (20-40 J.Lm), and are not suitable for our purpose.
MB-10 is a new package with a size distribution comparable to that of nannofossils.
Availability: MB-10, which will soon be widely available, is manufactured by Toshiba Ballotini
Company, a joint venture between Toshiba (Japan) and Potters Industries Inc. (USA), and Ballotini
is a trade name for their microbeads. You can buy MB-10 from distributors in various countries, andthe price will be ea 40,000 yen ($320) per 10 kg package. Unfortunately, no smaller pack is offered(at least in Japan), although you may not need more than a few hundred grams of the stuff for yourentire career. Please ask the following companies for the name of distributors.

Toshiba Ballotini Co. 3-3-10 Shiba, Minato-Ku, Tokyo 105, Japan.
Tel: 03-3455-2321; FAX: 03-3455-2923
Potter Industries Inc. 377 Route 17, South Hasbrouck Heights, NJ 07604, USA
Tel: 201-288-4700; FAX: 201-288-7696
Potters Ballotini Ltd. Pontefract Road, Barnsley, South Yorkshire, S71 1HJ, UK
Tel: 226-287591; FAX: 226-207615
Potters-Ballotini S. A. z.1. du Pont-Panay, Boite Postale 67, 03500, St. Pourcain-sur Sioule, France.
Tel: 70-45-9499; FAX: 70-45-5780
Potters-Ballotini Gmbh: Morschheimer Strasse 9, Postfach 1226, 6719, Kirchheimbolanden, Germany
Tel: 6352-8484; FAX: 6352-1853
PROCEDURE TO OBTAIN PROXY ABSOLUTE ABUNDANCE VALUE
1) Mix powdered sample with 5 to 10% (by weight) of the glass beads. If your sample is a nannoooze and tends to coagulate when wetted, mix a measured amount of carbonate-free clay to prevent
coagulation. Both the powdered sample and microbeads have to be accurately weighed. This requires
a precision balance with a resolution of 10·3g.
2) Place the mixture into a centrifuge (or test) tube and add an adequate quantity of buffered distilledwater.
3) Homogenize the muddy mixture by using a touch-mixer, and make a smear slide (or a spray slide
if you like). [N .B. touch-mixers are also referred to as spin-mixers and vortex-mixers, see anylaboratory catalogue for details].
4) Count the number of nannofossils under cross-polarized illumination (Fig. 1), and then count theglass beads in the same view-field under phase-contrast illumination (Fig. 2).
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INA Newsletter, 14/3 - 1992

Since smaller microbeads are difficult to recognize when mixed with clay minerals, anarbitrary cut-off point of 3 J.!.ID is recommended. According to the manufacturer, less than 8 % (byweight) of the beads are sn1aller than 3
in the MB-10 package.
S) Stop counting whencalculate thetally of glass beads reaches a predetermined number (e.g. 200 or 500), andI lOO beads ratio.

6) Convert the calculated ratio to a hypothetical standard ratio which is equivalent to the number ofnannofossils
100 glass beads if the mixing ratio of microbeads is 50 % by weight (t to 1mixture).
You can modify the bead:sample ratio to suit your preferences and the material. Then so long as step
6 is taken and we use the same glass bead package, we can compare other peopte•s abundance data
to our own. Moreover, if we can select a standard sample like PDB for oxygen isotope analysis, wecan use different products of microbeads and still express the observed abundance on a common scale;a percentage abundance to the standard sample. Does anybody have a candidate for the standard?

Fig. l.

Mlddl®

(llllll'kedMtl

Fig. 2. (right) The JWJW view

INA Newsletter, 14/3 - i992

rnmooi'lumbut lWUl'.detillumination. Three relatively large placollibs
The IICale bar in the lower right comet indicates 10p.m.
illu1niMtion. Five mierobeads a.re recogniuble u dark llphe:res.

97